function requestFullScreen() {
    if (isfull) {
      var de = document;
      if (de.exitFullscreen) {
          de.exitFullscreen();
      } else if (de.mozCancelFullScreen) {
          de.mozCancelFullScreen();
      } else if (de.webkitCancelFullScreen) {
          de.webkitCancelFullScreen();
      }
      isfull = false;
    } else {
      var de = document.documentElement;
      if (de.requestFullscreen) {
          de.requestFullscreen();
      } else if (de.mozRequestFullScreen) {
          de.mozRequestFullScreen();
      } else if (de.webkitRequestFullScreen) {
          de.webkitRequestFullScreen();
      }
      isfull = true;
    }
  }